U2 are making their latest comeback. Following Bono’s back surgery (which forced the cancellation of their North American tour), the group will hit the road in Europe for a series of dates and be back around the United States next summer.

U2 have had a fascinating career, as even though they’ve been one of the biggest bands in the world for the better part of the past three decades, they have still regularly been cast as underdogs on the comeback trail. Their story arc is remarkable, and it hit an interesting point when they released Pop in 1997.

When you consider most albums, you have to consider the context along with the songs. But in the case of Pop, it’s almost all about the context. The last time U2 had appeared, it was a part of the absolutely gigantic ZooTV tour, which at the time was one of the most ambitious stadium-sized rock shows ever produced.

It was in support of the hugely successful Achtung Baby, a moody art rock album masquerading as pop music (it helped that “One,” the one track on the album that doesn’t really fit, was a huge international hit). The band followed Achtung with a pair of strange experiments: 1993’s Zooropa, which was an album that leaned heavily on electronics and was written and recorded in between legs of ZooTV, and 1996’s Original Soundtracks 1, a heavily ambient album produced by Brian Eno and credited to Passengers (it was so out there that the label didn’t want them to release it under their own name).

That meant it had been nearly six years since a “proper” U2 album had been put on the market, so expectations were high. Those expectations were compounded by the fact that in the run-up to Pop’s release, people were suggesting that U2 had somehow managed to solve the conundrum that was facing rock music at the time.

Back in 1996, a reasonable portion of the population believed that dance music was going to take over as the next great underground genre to blow up to stadium size. Everybody was extremely excited about the Prodigy, and the Chemical Brothers were being treated like big time rock stars and not just a pair of DJs.

More and more bands were dipping into the electronic pool, augmenting their rock tunes with breakbeats, bits of trip-hop and whatever else floated over from the United Kingdom. It was seen as a conundrum that needed to be solved, as though somebody would eventually crack the code and deliver a song or an album that would successfully bring together the two disparate worlds to create a new genre.

Everybody was convinced that Pop was that album. Before anybody heard any music, people who thought about pop music for a living seemed to think that U2 had solved it, and when they dropped the single “Discotheque” a month before, it seemed like Pop was going to change everything. “Discotheque” grafted some super-distorted guitars, techno-funky bass and a sweaty breakbeat, and it still allowed for a killer chorus it sounded like the collision of modern dance music and rock and roll.

But when the album came out and fans listened to the other 11 songs on the album, there was much confusion. The first three songs on the album — “Discotheque,” “Do You Feel Loved” and “Mofo” — made an effort to attach disparate dance genres (like techno, house and drum and bass) to U2’s refined approach to stadium rock.

The problem is that none of those songs particularly succeed as dance songs or as rock workouts. “Discotheque” runs out of steam, “Do You Feel Loved” isn’t dynamic enough and “Mofo” devolves into a beat-happy mess.

And then U2 seem to abandon the premise entirely. Luckily, they do it for the sake of “If God Will Send His Angels” and “Staring at the Sun,” neither of which contain very much in the way of electronics but both of which contain blissful melodies and hypnotic hooks. (“If God Will Send His Angels,” in particular, seemed to be laying the groundwork for their throwback 2000 album All That You Can’t Leave Behind.) “Gone” is also a spectacular anthem with a giant chorus — in fact, Bono has a great time on Pop, as there are places for him to experiment as well as to hit his usual high notes. (Conversely, the Edge has the roughest time on Pop, as his guitar tones are often subverted, distorted or lost entirely.)

Latter day U2 albums also contain a healthy amount of obsessions with American culture, and Pop contains two such tracks: “Miami” and “The Playboy Mansion.” The former is an intense beat experiment that does a lot of swirling but doesn’t go much of anywhere, and “The Playboy Mansion” is about the closest thing the band has ever come to making a novelty song. Still, it’s charming in spots and has a jaunty little melody.

The album wraps up with the smoldering “If You Wear That Velvet Dress,” the lurching “Please” and the sparse, powerful “Wake Up Dead Man.” Really, those three songs act as a microcosm for U2’s entire career, as it has the right combination of romanticism, Catholicism, passion and darkness. Unfortunately, none of those songs have the sort of sweetness that lurks under even the most militant U2 tunes, which makes for a rather uneven finish to what ends up being a bizarre, disjointed album.

So Pop didn’t change the way we think about rock music, nor did it change the way we think about U2 (they ended up really coming back with All That You Can’t Leave Behind a few years later). Bono, the Edge, Adam Clayton and Larry Mullen, Jr. seemed to be distracted by keyboards and irony, which may explain why Pop is by far the most schizophrenic release in U2’s canon.

It’s an interesting entry in the band’s history (and a fascinating look at the state of rock music in 1997), but not up there with the essential All That You Can’t Leave Behind, Achtung Baby and The Joshua Tree.

One thing is for sure, U2 has created something that you can’t leave behind.